U.S. Pat. No. 5,270,638 discloses an inspection apparatus for inspecting polarities of poles of a DC voltage source. The inspection apparatus comprises two electric contacts which are connectable to the poles of the DC voltage source. The two electric contacts are connected to each other via a two-colored light emitting diode (LED) which outputs an optical signal depending on the polarity of the poles and the resulting current flow direction. For example, the LED glows red, if the polarity of the voltage present at one of the two electric contacts is positive with regard to the electric potential present at the other electrical contact. In case of an inversed polarity, the LED glows green. The inspection apparatus additionally comprises a further electric contact which, via a further two-colored LED, is connected to a voltage divider connected in parallel to the first two electric contacts. This further LED indicates the polarity of a voltage present at the further electric contact with regard to the average electric potential of the first two electric contacts.
CA 2,636,675 A1 discloses an inspection apparatus for inspecting polarities at an electric interface. The inspection apparatus comprises two electric contacts connected to each other via a signaling element. One of the two electric contacts is connectable to a voltage source, and the other electric contact is connectable to ground. The signaling element indicates the sign, e.g. the polarity of the voltage of the contact connected to the voltage source in that it outputs a signal depending on the current direction. The signaling element may, for example, comprise two anti-parallel LEDs.
U.S. Pat. Nos. 4,025,750, 3,600,678 and 4,233,560 each disclose an apparatus comprising a signaling element which in case of a polarity of an applied voltage matching a pre-set polarity is powered with an electric signal for outputting a matching signal. Further, each of these apparatuses comprises a switching element which blocks the matching signal from the signaling element in case the polarities do not match.
There still is a need of an inspection apparatus by which polarities of poles of a plurality of DC voltage sources individually connected to input terminals of a combiner circuit that are not yet connected to each other can be inspected easily.